Mail processing systems for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mail processing systems, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process thousands of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage meter requirements and other international postal regulations regarding closed system meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. A closed system is a system whose basic components are dedicated to the production of information-based indicia and related functions, similar to an existing, traditional postage meter. A closed system, which may be a proprietary device used alone or in conjunction with other closely related, specialized equipment, includes the indicia print mechanism.
The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. An example of such an indicium is illustrated in FIG. 1. The indicium 10 consists of a two-dimensional (2D) barcode 12 and certain human-readable information 14. Some of the data included in the barcode can include, for example, the PSD manufacturer identification, PSD model identification, PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing. In addition, a digital signature is required to be created by the PSD for each mail piece and placed in the digital signature field of the barcode. Verification of indicium is performed by the postal service scanning a mail piece to read the 2D barcode and verifying the information contained therein, including the digital signature. If the verification is unsuccessful, indicating that the indicium may not be authentic, the mail piece may not be delivered.
Since postal services accept indicia printed by mail processing systems as conclusive proof of payment of the amount of postage indicated, such devices are in effect machines for printing money. As a result postal services have imposed high standards for the print quality of indicia images produced by such machines, including, for example, resolution of the image. Even if an indicium is valid, if the verification equipment is unable to read the indicium due to poor print quality, verification will not be possible. It is therefore necessary to ensure that the printing systems utilized by the mail processing systems are capable of consistently producing high quality images.
In recent years, ink jet printing systems have been utilized in mail processing systems. Ink jet printing systems, as used herein, includes any form of printing wherein print control signals control a print mechanism to eject ink drops to produce a matrix of pixels, i.e. picture elements, to represent an image. An ink supply, typically in the form of a reservoir, supplies ink to the print mechanism. As the ink supply is depleted, it must be replaced by an operator. The cost for periodically replacing the ink supply can be significant, especially for high volume mail processing systems that can process 20,000 mail pieces or more per hour and typically operate for twenty-four hours every day for extended periods of time. As such, it is desirable to utilize the minimum amount of ink necessary for each indicium, while still meeting the print quality requirements to ensure each indicium can be read. The printing system can be set to a resolution of, for example, 200×300 dpi, i.e., 200 per inch horizontal resolution and 300 dots per inch vertical resolution. This resolution will provide sufficient contrast with respect to a typical medium, i.e., mail piece, upon which an indicium will be printed, such as, for example, a white envelope. This resolution, however, may not provide sufficient contrast if a darker medium is used, such as, for example, manila or gray envelopes, where a higher resolution in the vertical direction is required. For darker colored mail pieces, it may be necessary to have a higher resolution, such as, for example, 200×600 dpi, to provide sufficient contrast for the indicium to be properly read. Setting the printing system to the higher resolution, however, uses more ink per indicium than the lower resolution. Thus, if the resolution is set based on the darker medium, it will result in a significant amount of ink being wasted when printing on the lighter medium, as the extra ink is not necessary to meet the contrast requirements. The extra unnecessary ink required can significantly increase the cost of operating the mailing machine.
Thus, there exists a need for a method and system that reduces the amount of ink consumption required for printing while still meeting the required print quality standards for different mediums.